NASA Technical Reports Server (NTRS) 20110023859: Tilt-Sensitivity Analysis for Space Telescopes

9 Books & Reports

$ Analysis of Designs of Space
Laboratories

A report presents a review of the de-
velopment of laboratories in outer
space, starting from the pioneering Sky-
lab and Salyut stations of the United
States and the former Soviet Union and
progressing through current and antic-
ipated future developments. The report
includes textual discussions of space-
station designs, illustrated with draw-
ings, photographs, and tables. The ap-
proach taken in the review was not to
provide a comprehensive catalog of
each space laboratory and every design
topic that applies to it, but, rather, to il-
lustrate architectural precedents by
providing examples that illustrate
major design problems and principles
to be applied in solving them. Hence,
the report deemphasizes information
from the most recent space-station lit-
erature and concentrates on informa-
tion from original design reports that
show how designs originated and
evolved. The most important contribu-
tion of the review was the development
of a methodology, called “units of
analysis,” for identifying and analyzing
design issues from the perspectives of
four broad domains: laboratory sci-
ence, crew, modes of operations, and
the system as a whole.

This work was done by Marc M. Cohen of
Ames Research Center. Further informa-
tion is contained in a TSP ( see page 1 ).
ARC-14965

$ Shields for Enhanced
Protection Against High-
Speed Debris

A report describes improvements
over the conventional Whipple shield
(two thin, spaced aluminum walls) for
protecting spacecraft against high-
speed impacts of orbiting debris. The
debris in question arises mainly from
breakup of older spacecraft. The im-
proved shields include exterior
“bumper” layers composed of hybrid
fabrics woven from combinations of ce-
ramic fibers and high-density metallic
wires or, alternatively, completely metal-
lic outer layers composed of high-
strength steel or copper wires. These

shields are designed to be light in
weight, yet capable of protecting
against orbital debris with mass densi-
ties up to about 9 g/cm 3 , without gen-
erating damaging secondary debris par-
ticles. As yet another design option,
improved shields can include sparsely
distributed wires made of shape mem-
ory metals that can be thermally acti-
vated from compact storage containers
to form shields of predetermined shape
upon arrival in orbit. The improved
shields could also be used to augment
shields installed previously.

This work was done by Eric L. Chris-
tiansen and Justin H. Kerr of Johnson
Space Center. Further information is con-
tained in a TSP (see page 1 ).

This invention is owned by NASA, and a
patent application has been filed. Inquiries
concerning nonexclusive or exclusive license
for its commercial development should be ad-
dressed to the Patent Counsel, Johnson Space
Center, (281 ) 483-0837. Refer to MSC-22330.

Study of Dislocation-
Ordered In*Gai_*As/ GaAs
Quantum Dots

A report describes an experimental
study of dislocation-induced spatial or-
dering of quantum dots (QDs) compris-
ing nanometer-sized In x Gai_ x As islands
surrounded by GaAs. Metastable hetero-
epitaxial structures were grown by mole-
cular-beam epitaxy of In x Gai_ x As onto n +
GaAs and semi-insulating GaAs sub-
strates. Then the structures were relaxed
during a post-growth annealing/self-or-
ganizing process leading to the forma-
tion of surface undulations that acted as
preferential sites for the nucleation of
QDs. Structural effects of annealing
times and temperatures on the strain-re-
laxed In x Gai_ x As/GaAs and the subse-
quent spatial ordering of the QDs were
analyzed by atomic-force microscopy and
transmission electron microscopy. Con-
tinuous-wave spectral and time-resolved
photoluminescence (PL) measurements
were performed to study the effects,
upon optical properties, of increased QD
positional ordering, increased QD uni-
formity, and proximity of QDs to arrays
of dislocations. PL spectral peaks of or-
dered QD structures formed on strain-re-
laxed In x Gai_ x As/ GaAs layers were

found to be narrower than those of struc-
tures not so formed and ordered. Rise
and decay times of time-resolved PL were
found to be lower at lower temperatures
— apparently as a consequence of de-
creased carrier-transport times within
the barriers surrounding the QDs.

This work was done by Rosa Leon of Cal-
tech for NASA’s Jet Propulsion Labora-
tory. Further information is contained in a
TSP (seepage 1 ).

NPO-30691

Tilt-Sensitivity Analysis for
Space Telescopes

A report discusses a computational-
simulation study of phase-front propa-
gation in the Laser Interferometer
Space Antenna (LISA), in which space
telescopes would transmit and receive
metrological laser beams along 5-Gm
interferometer arms. The main objec-
tive of the study was to determine the
sensitivity of the average phase of a
beam with respect to fluctuations in
pointing of the beam. The simulations
account for the effects of obscurations
by a secondary mirror and its support-
ing struts in a telescope, and for the ef-
fects of optical imperfections (espe-
cially tilt) of a telescope. A significant
innovation introduced in this study is a
methodology, applicable to space tele-
scopes in general, for predicting the ef-
fects of optical imperfections. This
methodology involves a Monte Carlo
simulation in which one generates
many random wavefront distortions
and studies their effects through com-
putational simulations of propagation.
Then one performs a statistical analysis
of the results of the simulations and
computes the functional relations
among such important design parame-
ters as the sizes of distortions and the
mean value and the variance of the loss
of performance. These functional rela-
tions provide information regarding
position and orientation tolerances rel-
evant to design and operation.

This work was done by Miltiadis Pa-
palexandris of Caltech and Eugene
Waluschka of Goddard Space Flight Center
for NASA’s Jet Propulsion Laboratory.
Further information is contained in a TSP
(see page 1 ).

NPO-30709

NASA Tech Briefs, July 2003

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